The present disclosure relates generally to fluid distribution systems and, more particularly, to diagnostic systems for use with fluid distribution systems and methods of diagnosing such systems.
In agricultural spraying, the flow rate through a spray nozzle is an important factor in delivering a specified amount of agrochemical to a specified area. Most agrochemicals such as crop protection agents and many fertilizers are applied as liquid solutions, suspensions, and emulsions that are sprayed onto the target fields. Certain agrochemicals, such as anhydrous ammonia, are dispensed into soil through dispensing tubes positioned behind knives or plows that prepare the soil for application.
Typically, the agrochemical liquid is supplied by powered pumps to simple or complex orifice nozzles that atomize the liquid stream into spray droplets. Nozzles are often selected primarily on the desired range of flow rates needed for the job and secondarily on the range of liquid droplet size spectra and spray distribution patterns they produce.
Increasing concerns over inefficient agrochemical use, the cost of agrochemicals and inadvertent spray drift or pesticide run-off have resulted in attempts to improve the quality, precision, accuracy and reliability of application of agrochemicals. This has led to increased use of electronic control systems and GPS-guided operations. Growth in these “precision agriculture” products and strategies has led to greater demand for “variable rate” technologies and the fluid handling means to alter spray liquid flow rates.
New sprayer models may have booms of 30 m (approximately 90 ft) widths and allow application at speeds up to 30 km/hr (20 mph) or higher. Faster ground speeds and wider spray booms can lead to application errors that are significant yet unavoidable with existing spray technology. For example, if the sprayer is traversing the edge of a field while scribing about a 100 m radius (actually, a very gentle turn), the outer nozzles are traveling 35% faster than the inner nozzles. At a 50 m radius, the difference in nozzle ground speeds is 85%. With sharp turns, such as at the end of a pass, the inner nozzles will travel backwards, thereby retracing and overdosing previously sprayed areas, while the outer nozzles will significantly accelerate giving their associated land areas sparse coverage of chemical. Unless the flow rate from each nozzle is individually adjusted to compensate for these differences in travel speeds, application errors may occur.
Individual control of spray nozzles or nozzle assemblies is of growing importance in agrochemical application. As individual control increases, the need for individual flow monitoring will increase since feedback is often needed for closed loop control. Even with a linear control strategy, such as the binary control of multiple nozzles or pulse width modulation, confirmation of proper flow is important.
As the spray application industry adopts larger liquid storage tanks on mobile equipment, operators are likely to make fewer stops for refilling and cover greater land area between stops. Consequently, clogged nozzles or other problems on the boom are unlikely to be detected while significant land areas are being treated. For example, assuming a 30 km/hr ground speed, a 30 m boom width and 50 l/ha (apprx. 5 gal/acre) application rate, a 4000 l (apprx. 1000 gal) tank will cover 200 acres in apprx. 1 hour. A single nozzle in this example would treat apprx. 3.5 acres per tank load and a single undetected nozzle malfunction would correspond to this 3.5 acre area receiving an incorrect, or perhaps zero, dose of agrochemical.
Additionally, wider boom widths, travel speeds and vehicle sizes increasingly restrict an operator's view of the boom and the opportunities to view the boom while driving. On modern agricultural spray vehicles, 30 to 50% of the spray boom may not be visible to the operator.
On some larger sprayers such as those typically used by custom applicators in the Midwest, Central Canada and the Plains, video cameras are sometimes mounted on the rear of the sprayer so that the operator can monitor, at least in theory, the spray boom out of his or her line of sight. However, at high travel speeds, the operator's attention is fully devoted to driving instead of monitoring the spray boom in the rear, either in the line of direct sight or shown on the video monitor. Due to poor overall visibility from the operator's station and the infrequency of stops and refillings, there is a need for individual nozzle monitoring to confirm that no clogging, pinched hoses, damaged nozzles or other problems may be present or developing on the spray boom.
A similar problem exists on shielded or shrouded sprayers sometimes used in the North American Plains and in urban and landscape applications. In farming areas in extreme southern and northern latitudes and in high value specialty crops, often grown in coastal areas, the agronomic time window for pesticide applications can be critically short and often occurs during windy periods. Shielded sprayers are often used in these conditions. Similarly, sprayers used in golf course, landscape and other urban conditions commonly use shrouds, curtains or shields to reduce spray drift and as a concession to public relations. However, the shields prevent the operator from visually inspecting the nozzle spray patterns to confirm proper operation. Improperly operating nozzles are not easily detected. Commercial systems for agricultural use often address this problem by routing individual liquid lines to each nozzle through a small rotameter (ball in tube) flow monitor that is mounted in the operator's line of sight. Such rotameters require cumbersome plumbing for each nozzle and require the operator visually monitor the bank of tubes.
One drawback of relying on visual inspection (either direct line of sight or video) or simple flow measurement (ball in tube) is that such methods do not assure proper nozzle operation. Nozzles can be partially clogged or have an obstruction in the flow path and appear to be operating correctly even if the flow rate is significantly affected. Conversely, the nozzle pattern and spray droplet size can be severely distorted by an obstruction or damage, yet the flow rate remains close to the original value.
Electronic spray rate control systems and application monitors typically use a single flowmeter and/or pressure transducer for feedback of the flow conditions on the entire spray boom. In systems with many nozzles, such as a 50-60 nozzle boom, failure of 1 or 2 nozzles would be unlikely to raise an alarm since the overall effect is only 2% of the expected flow rate; the system would compensate by maintaining the correct overall flow to the entire boom. So, if one nozzle became completely clogged, the system would simply increase the spray pressure and force an additional 20% flow through the remaining nozzles operating properly. Even with the electronic control or monitor system, the driver would likely remain unaware of the failure.
Additionally, when individual nozzle control is implemented, the need for individual nozzle monitoring increases. Pulse width modulation systems have electrical and mechanical components on each nozzle. Multiple nozzle manifolds have multiple tips and actuators at each boom location. The opportunity for failure is increased over that of a simple nozzle. These systems require not only flow monitoring but also monitoring of the control actuators used for flow or droplet size modulation. Moreover, individual nozzle control implies that individual nozzle feedback is required for closed loop operation.
Future systems may incorporate individual nozzle injection of multiple agrochemicals or adjuvants, individual control of droplet size spectra, droplet velocity or spray distribution. In each case, the need for monitoring and actuation on a single-nozzle or single manifold basis increases.
Thus, a need currently exists for a system and process for monitoring spray nozzle operation. Such a system and process is well suited for use in the agricultural field. It should be understood, however, that similar needs also exist in other fields. For example, on irrigation systems, there may be many small nozzles, often obscured from view or in areas that are difficult to access. Failure of a nozzle might not be detected until drought damage to a plant had occurred and symptoms were visible. Likewise, in industrial spray driers, malfunction of a nozzle might not be detected until significant amounts of product had been damaged. In spray humidification or cooling systems, nozzle failures might not be detected until excessive heating or drying had occurred. Specifically, a system that monitors nozzle operation may find wide applicability in any system, whether commercial, industrial or residential, that utilizes spray nozzles.